An electric fan for cooling the radiator of a motor vehicle typically comprises a direct-current electric motor and an axial fan which are both supported by a cowling which has the dual functions of optimizing the air flow downstream of the radiator and securing the motor/fan unit to the radiator or to another support provided in the motor vehicle.
In more advanced systems, the direct-current motor may be a motor having brushes which is associated with an electronic control unit or an electronic commutation or brushless motor also with an electronic control unit.
When operating axial fans at maximum speed the volume flow rate decreases with increasing pressure of the air and the torque needed and therefore, the electrical power required, increases (for the same number of revolutions) as the pressure increases.
With a stationary car, there is the maximum value of fluid-dynamic resistance and therefore the minimum value of air capacity. If the velocity of the car increases, the capacity of available air increases because the resistance decreases owing to the effect of the pressure caused by the velocity of the car itself. This behavior is counter to the natural need for cooling of the car because normally the thermal flux to be discharged increases when the car is moving.
In the case of a commutator motor being supplied with constant voltage, the speed at which the fan rotates decreases as the pressure itself increases owing to the greater power required.
The behavior in the case of an electronic commutation motor may be similar to that of a commutator type motor, or the controller may maintain a constant velocity for the entire range of operating pressure.
If a system being examined has insufficient capacity at low pressures and a capacity greater than requirements at high pressures, a simple solution for achieving the effectiveness required even at low pressures is to increase the velocity of the fan under those conditions. In that manner, the capacity curve extends upwards. The electrical power required increases accordingly. The result of such an action involves sizing the electric motor and the electronic control unit for far greater power levels, which involves higher costs for the product.
Furthermore, it is not always possible to follow this path because a maximum limit of power absorbed is fixed for reasons of dimensions and energy balance of the electrical system and in order to limit the emissions of pollutants and the consumption of the car.
The present invention specifically relates to a control device comprising: at least one control transistor which is substantially connected in series to a corresponding winding of the motor between the terminals of a direct-current supply voltage source; and an electronic control unit which is provided to control the at least one transistor in accordance with predetermined manners in accordance with at least one external control signal so as to bring about the actuation of the motor by controlling the voltage applied thereto and consequently, the velocity of the fan.
Such a control device is schematically illustrated in FIG. 1 of the appended drawings. In that Figure, there is generally designated 1 a cooling electric fan for an internal-combustion engine comprising a direct-current electric motor M of the type with brushes and an associated bladed fan rotor F. The motor M is substantially connected in series to a control transistor Q, for example, a transistor of the MOSFET type, between the two terminals or poles of a source (for example, a battery) S, which is able to distribute a direct-current supply voltage VS. The input or gate of the control transistor Q is connected to the output of an electronic control unit ECU which is provided to control the transistor in predetermined manners in accordance with at least one external control signal.